1. Field of the Invention
This invention relates to a projecting exposure apparatus. This invention particularly relates to a projecting exposure apparatus, wherein a two-dimensional pattern of light having been obtained from spatial light modulation is projected through a telecentric image forming optical system onto a photosensitive material, and the photosensitive material is thus exposed to the two-dimensional pattern of the light.
2. Description of the Related Art
Projecting exposure apparatuses, wherein spatial light modulation means for performing spatial light modulation of incident light in accordance with a predetermined control signal is utilized, a two-dimensional pattern of the light, which has been obtained from the spatial light modulation performed by the spatial light modulation means, is projected onto a photosensitive material, and the photosensitive material is thus exposed to the two-dimensional pattern of the light, have heretofore been known. Also, projecting exposure apparatuses, wherein a digital micromirror device (hereinbelow referred to as the DMD) comprising a plurality of (e.g., 1,024×756) micromirrors, which allow alteration of their inclination angles and which are arrayed in a two-dimensional pattern, is utilized as the spatial light modulation means, have heretofore been known. (The projecting exposure apparatuses, wherein the digital micromirror device (DMD) is utilized as the spatial light modulation means, are described in, for example, Patent Literature 1.) As the digital micromirror device (DMD), for example, a DMD supplied by Texas Instruments Co. has been known. Projectors for dynamic images, wherein the DMD is utilized, and the like, have been used in practice.
The projecting exposure apparatuses utilizing the DMD are provided with an image forming optical system for forming an image of each of the micromirrors of the DMD on the photosensitive material. With the projecting exposure apparatuses utilizing the DMD, the images of only the light, which has been reflected from certain micromirrors inclined at predetermined angles among the micromirrors that receive the irradiated light for exposure, and which travels toward the image forming optical system, are formed through the image forming optical system. In this manner, the two-dimensional pattern having been formed by the micromirrors is projected onto the photosensitive material, and the photosensitive material is thus exposed to the two-dimensional pattern. Specifically, with the projecting exposure apparatuses utilizing the DMD, the exposure operation is performed such that each of pixels constituting the image of the two-dimensional pattern corresponds to one of the micromirrors.
The projecting exposure apparatuses described above is provided with an exposure head for irradiating the two-dimensional pattern to the photosensitive material. By way of example, as illustrated in FIG. 20, optical elements constituting the exposure head include a DMD 80J, and a light source unit 60J for producing the light to be irradiated to the DMD 80J. The optical elements constituting the exposure head also include a DMD irradiation optical system 70J provided with a total reflection prism 76J for receiving the light, which has been radiated out from the light source unit 60J, and totally reflecting the light toward the DMD 80J, and an optical system 50J for forming an image of the two-dimensional pattern of the light, which has been obtained from spatial light modulation performed by the DMD 80J, on a photosensitive material 150J.
The optical system 50J described above comprises a first image forming optical system 51J. The optical system 50J also comprises a second image forming optical system 52J for relaying the image of the two-dimensional pattern, which image has been formed by the first image forming optical system 51J, and forming the image of the two-dimensional pattern on the photosensitive material 150J. The optical system 50J further comprises a microlens array 55J and an aperture array 59J, which are located in the optical path between the first image forming optical system 51J and the second image forming optical system 52J.
The microlens array 55J described above is constituted of a plurality of microlenses 55Ja, 55Ja, . . . Each of the microlenses 55Ja, 55Ja, . . . is located at a position corresponding to one of micromirrors 81J, 81J, . . . of the DMD 80J, such that the microlens 55Ja transmits and converges a telecentric light beam Lj corresponding to one of the micromirrors 81J, 81J, . . . , which light beam has been reflected from the corresponding micromirror 81J of the DMD 80J and has passed through the first image forming optical system 51J. Also, the aperture array 59J comprises a plurality of apertures 59Ja, 59Ja, . . . Each of the apertures 59Ja, 59Ja, . . . is located at a position corresponding to one of the microlenses 55Ja, 55Ja, . . . of the microlens array 55J, such that the aperture 59Ja allows the passage of the light beam, which has passed through the corresponding microlens 55Ja of the microlens array 55J.
In the optical system 50J having the constitution described above, each of telecentric light beams Lj, Lj, . . . corresponding respectively to the micromirrors 81J, 81J, . . . of the DMD 80J, which light beam has passed through the first image forming optical system 51J after being reflected from the corresponding micromirror 81J, is collected by the corresponding microlens 55Ja of the microlens array 55J, which is located on the side of the first image forming optical system 51J and in the vicinity of the position of image formation with the first image forming optical system 51J. Each of the light beams Lj, Lj, . . . , which light beam has thus been collected by the corresponding microlens 55Ja, passes through the corresponding aperture 59Ja.
Each of the light beams Lj, Lj, . . . , the image of which light beam has been formed by the first image forming optical system 51J, passes through the microlens array 55J and the aperture array 59J. Each of the light beams Lj, Lj, . . . is then relayed by the second image forming optical system 52J, and the image of the light beam Lj is formed on the photosensitive material 150J. In this manner, the two-dimensional pattern is projected onto the photosensitive material 150J, and the photosensitive material 150J is thus exposed to the two-dimensional pattern.
In cases where each of pixels constituting the image of the two-dimensional pattern, i.e. each of the light beams Lj, Lj, . . . , which have passed through the corresponding microlenses 55Ja, 55Ja, . . . after being reflected from the corresponding micromirrors 81J, 81J, . . . , undergoes thickening due to aberrations of the optical elements described above, and the like, the light beam Lj is capable of being shaped by the corresponding aperture 59Ja such that the spot size on the photosensitive material 150J becomes identical with a predetermined size. Also, as described above, each of the light beams Lj, Lj, . . . , which light beam has been reflected from one of the micromirrors 81J, 81J, . . . is passed through the aperture 59Ja, which corresponds to the micromirror 81J. Therefore, cross talk between the micromirrors 81J, 81J, . . . (i.e., between the pixels constituting the image of the two-dimensional pattern) is capable of being prevented from occurring, and the extinction ratio in on-off operations of each of the micromirrors 81J, 81J, . . . at the time of the exposure operation is capable of being enhanced. Accordingly, the contrast of the two-dimensional pattern projected onto the photosensitive material 150J is capable of being kept high, and the quality of the exposure operation is capable of being enhanced.
The state, in which each of the micromirrors 81J, 81J, . . . is inclined at the predetermined angle such that the light beam having been reflected from the micromirror 81J travels toward the optical system 50J, is the on state of the micromirror 81J. Also, the state, in which each of the micromirrors 81J, 81J, . . . is inclined at an angle different from the predetermined angle such that the light beam having been reflected from the micromirror 81J travels along a direction shifted from the direction of the optical path heading toward the optical system 50J, is the off state of the micromirror 81J. The image of the light beam, which has been reflected from the micromirror 81J in the on state, is formed on the photosensitive material 150J, and the photosensitive material 150J is thus exposed to the light beam. Therefore, the extinction ratio may be defined as the ratio of the brightness of the pixel region corresponding to a micromirror 81J, which pixel region is formed on the photosensitive material 150J when the micromirror 81J is set in the off state, to the brightness of the pixel region corresponding to the micromirror 81J, which pixel region is formed as an image on the photosensitive material 150J when the micromirror 81J is set in the on state.
[Patent Literature 1]                Japanese Unexamined Patent Publication No. 2001-305663        
However, there is a strong demand for a projecting exposure apparatus, wherein the extinction ratio and the exposure quality are capable of being enhanced even further. In order for the extinction ratio and the exposure quality to be enhanced even further, for example, it is required that each of the telecentric light beams Lj, Lj, . . . , which light beam has passed through the first image forming optical system 51J after being reflected from the corresponding micromirror 81J among, for example, 1,024×256 (approximately 260,000) micromirrors 81J, 81J, . . . constituting the DMD 80J in the constitution described above, is capable of being transmitted more accurately through a microlens 55Ja among the 1,024×256 microlenses 55Ja, 55Ja, . . . , which microlens 55Ja corresponds to the micromirror 81J, and an aperture 59Ja among the 1,024×256 apertures 59Ja, 59Ja, . . . , which aperture 59Ja corresponds to the micromirror 81J, and that the image of the telecentric light beam Lj is thus capable of being formed. Specifically, it is necessary that the pitches among the approximately 260,000 telecentric light beams Lj, Lj, . . . , each of which travels to one of the microlenses 55Ja, 55Ja, . . . and one of the apertures 59Ja, 59Ja, . . . , are capable of being set to coincide with the pitches among the same number of the corresponding microlenses 55Ja, 55Ja, and the pitches among the same number of the corresponding apertures 59Ja, 59Ja, . . . , and that the thickening of each of the telecentric light beams Lj, Lj, . . . and errors in parallelism of the telecentric light beams Lj, Lj, . . . with respect to one another are capable of being suppressed. For such purposes, it is desired that the characteristics of the first image forming optical system 51J, such as modulation transfer function (MTF) performance (suppression of the thickening of the light beams), telecentric characteristics (parallelism of the light beams with respect to one another), distortion performance (equi-pitch characteristics), and the accuracy of the magnification of image formation, are capable of being enhanced to predetermined characteristics such that the desired exposure quality is capable of being obtained.
However, the characteristics described above (i.e., the MTF performance, the telecentric characteristics, the distortion performance, and the accuracy of the magnification of image formation) have correlations with one another. For example, if the accuracy of the magnification of image formation is enhanced, it will occur that the MTF performance and the distortion performance become bad. Therefore, the problems occur in that the first image forming optical system 51J cannot always be produced such that all of the characteristics described above become identical with at least the predetermined characteristics.